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Corning® Assay Surfaces Corning offers a variety of modified polystyrene surfaces for the binding or covalent immobilization of cells, proteins, nucleic acids, and other types of biomolecules for use in microplate-based assays that do not require cell attachment (see Table 1). Check Corning® Cell Culture Surfaces for information on assay surfaces for cell-based assays. Choosing the appropriate assay surface requires that the structure of the molecule to be immobilized be known, so that functional groups available on the molecule can be matched with the correct surface. Of particular concern is that the functional group on the biomolecule interacting with the surface must be positioned in such a manner that immobilization does not interfere with its immunological or enzymatic activity. Table 1. Corning® microplate assay surfaces
Overview The first 96 well microplates were manufactured from a variety of plastic resins in the 1950's for use in virus titration studies. By the mid 1960's, most of these microplates were made from polystyrene, a long carbon chain polymer with benzene rings attached to every other carbon. Polystyrene was chosen because it has excellent optical clarity, is easy to mold and is relatively inexpensive. In addition, the normally hydrophobic surface of polystyrene can be easily modified by a variety of chemical and physical (corona discharge, gas-plasma or irradiation) methods to make the surface hydrophilic and thus suitable for cell attachment and culture (Figure 1). By the late 1970's, these microplates were also being used as reaction vessels for Enzyme-Linked Immunosorbent Assays (ELISA) which require surfaces suitable for immobilizing proteins and other biomolecules. By altering the chemical and physical surface treatment methods, a variety of chemical groups can readily be grafted onto the polymer to allow the covalent attachment of a variety of reactive groups for the subsequent covalent immobilization of biomolecules. Corning offers microplates in a wide variety of formats and well designs (see Table 2).
Immobilization Mechanisms Proteins and other biomolecules attach to surfaces by several different mechanisms. (Please refer to Corning Technical Bulletin Immobilization Principles - Selecting the Surface for additional information.) Passive adsorption consists of primarily hydrophobic interactions or hydrophobic/ionic interactions between the biomolecules and the surface. Typical nomenclature for passive binding surfaces includes Medium Binding (Untreated) for hydrophobic surfaces and High Binding for surfaces that are modified to have a small number of ionic carboxyl groups resulting in a slightly ionic, hydrophobic surface. Covalent immobilization to polystyrene can be accomplished through several means. On surfaces that are aminated or carboxylated, covalent coupling is achieved using bifunctional crosslinkers that couple the amine or carboxyl group on the surface to a functional group, such as an amine or sulfhydryl, on the biomolecule. Selection of the crosslinker determines the type of covalent bond that will be formed. Functional and covalently reactive groups, such as N-oxysuccinimide, maleimide and hydrazide groups, can also be grafted onto a polystyrene surface. These reactive groups are coupled to the polystyrene via a photolinkable spacer arm resulting in a stable, yet reactive surface. |
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